A camera including a plurality of imaging units in one camera apparatus (a so-called compound eye camera) can image the identical subject from a plurality of viewpoints. Thus, the compound eye camera can be used for acquiring three-dimensional information of a subject. In a field of film appreciation, there is appreciation media for a three-dimensional picture such as a print which is made by using images acquired from the respective imaging units and having parallaxes, and is implemented by using a lenticular lens sheet. The compound eye camera is used as an image input device for the media.
As described above, the compound eye camera includes the plurality of imaging units. Accordingly, favorable parallax images cannot be acquired under a condition in which there are variations in characteristics of a lens, an imaging element or the like of each imaging unit or variations in the placement attitude on an imaging unit-by-imaging unit basis when mounting the imaging units. In particular, the latter variations greatly influence the parallax information. Thus, it is important to reduce the variations in placement attitudes of the imaging units for the sake of prevention of degrading a stereoscopic effect and viewability of the three-dimensional image.
When a subject (person) SUB2 is imaged by two imaging units (left and right) as shown in FIG. 12A, it is difficult to acquire ideal parallax images. The ideal parallax images IMGL and IMGR are imaged under a condition without variations in the attitude of the imaging units in the camera, and between the ideal parallax images IMGL and IMGR, the image SUB2L of the subjects SUB in the image IMGL imaged by the left imaging unit and the image SUB2R of the subject SUB2 in the image IMGR imaged by the right imaging unit are displaced each other toward a horizontal direction of the images IMGL and IMGR, the displacement being due to the parallax, as shown in FIG. 12B. In actually-acquired parallax images IMGL′ and IMGR′, the image SUB2L′ and SUB2R′ of the subject SUB2 in the images IMGL′ and IMGR′ are displaced due not only to parallax, but also to the attitudes of the imaging units (FIG. 12C).
In a process of manufacturing the compound eye camera, it is preferable that the imaging units are mounted with high location precision so as to eliminate the above-mentioned displacement of the image of the subject due to the variations of the attitudes of the imaging units. However, the pursuit of precision causes problems of reduction in productivity, increase in operation worker-hour and the like.
In order to solve the above described problems, conventionally, PTL 1 and PTL 2 suggest methods which eliminate a difference in geometrical characteristics between the imaging units by geometrically transforming images taken by the compound eye camera.
In a method described in PTL 1, in order to correct projective distortions caused by displacement in positions and attitudes of the plurality of cameras, images taken by the respective cameras are projected on the same (single, identical) plane, and the images taken by the respective cameras are corrected to be the images on the same plane.
A method described in PTL 2 is suggested to correct deviations caused by differences in attitudes and zoom factors of the imaging units among deviations in angles of view which arise when two imaging units simultaneously take images of a subject. In the method described in PTL 2, corresponding points between images acquired by the respective imaging units are detected, calculates a geometrical correction parameter such that the corresponding points of respective images are identical to each other, and transforms the images using the parameter.